The invention relates to an appliance for preparing an infusion from a fill of substance in powder or pod form, the appliance comprising a case including an infusion head containing a chamber that presents an opening through which the fill can be inserted, that presents an end wall with a hot water feed nozzle, and that is fitted with a closure part having an infusion outflow orifice, the closure part being movably mounted relative to said chamber to occupy two positions, an open position or a closed position, corresponding respectively to filling/emptying said chamber, and to preparing the infusion, the case also having a water container communicating with said nozzle.
More precisely, the invention relates to an appliance in which the case has a body including pressurizing means with an active state and an inactive state and designed, in the active state, to deliver air for the purpose of pressurizing said water container, and control means suitable for causing a certain volume of water raised to an infusion temperature to be delivered from said container into the infusion chamber.
An appliance of that type is described for example in the French patent application filed by the Applicant on Feb. 1, 2006, under the No. 06/00910.
Although that type of appliance produces a satisfactory infusion from a fill of coffee, it is found during infusion cycles that, for a given quantity of grounds, the pressure delivered by the air pump follows a slow progressive curve starting from a low pressure on starting and rising to a high pressure in a final stage. In order to maintain that pressure, it is therefore necessary to operate the pump before and throughout the infusion cycle, thereby leading to a non-negligible level of energy consumption on that type of manual appliance. In addition, when making an infusion of coffee, this progressive rise in pressure is not the best way of extracting all of the aroma from the coffee grounds. It happens that during the starting stage, and because of the low pressure, the water leaves the container at low pressure and at a low flow rate so that only the top layer of the grounds become soaked in water, whereas the majority of the grounds are merely moistened and do not have the time to expand in full. Thereafter, the water tends to pass through that majority via multiple interstices or paths that are being created, without impregnating the grounds sufficiently to extract all of the aroma therefrom. As a result after a certain lapse of time, once the pressure reaches the maximum threshold as determined by the manufacture, the hot water follows the preferred paths and flows strongly but without causing the grounds to swell sufficiently.
As described in patent application US 2006/0230946, an improvement is also known relating to pressurizing the water container, which improvement consists in associating a compression chamber with the pressurizing means, the compression chamber being arranged between said pressurizing means and said water container and including inlet and outlet isolation means. However that application does not solve the above-mentioned problem.